Outlook of Critical Habitats in the Western Indian Ocean: Salt marshes Janine Adams1 and Salomão Bandeira2 1 Department of Botany and Nelson Mandela University, PO Box 77000, Port Elizabeth, South Africa, 6031. 2 Department of Biological Sciences, Universidade Eduardo Mondlane, PO Box 257, Maputo, Mozambique Background Salt marshes are defined as “areas, vegetated by herbs, grasses or low shrubs, bordering saline water bodies (Adam et al. 1990). They are subjected to periodic flooding as a result of fluctuations (tidal or non- tidal) in the level of the adjacent water body”. Salt marshes occur in arctic and temperate regions, as well as in the subtropics and tropics where they occur in areas where mangrove development is precluded, or as a component of a salt marsh-mangrove ecotone (Adam 1990). Macnae (1969) stated that in drier regions where rainfall is seasonal, the lower tidal range is occupied by mangroves and the higher shore line by salt marsh. This is supported by the distribution of salt marshes in the tropics and northern Africa where this habitat replaces mangroves where the sediment is too dry or saline. In the subtropical estuaries of South Africa mangroves occupy the lower tidal zone and salt marshes occur in the higher, drier areas (Figure 1, Adams et al. 2016). Sometimes this is a very narrow band and therefore difficult to map as a separate habitat. In addition, according to Adam (1990), on arid or strongly seasonal tropical / subtropical coasts salt marshes may not extend upwards to the highest tide level, but may be fringed on their landward side by extensive hypersaline flats, known in the Middle East as sabkha. These areas exist in the WIO region but have not been described in detail. In Africa salt marshes are described for the Mediterranean, north west, south and south west coasts. Mcowen et al. (2017) defined salt marshes as “tidal communities that comprise the upper, vegetated portion of intertidal mudflats, lying approximately between mean high water neap tides and mean high water spring tides”. Other global definitions of salt marshes also only consider tidal systems (e.g. Best et al. 2007; Weis and Butler 2009). However, in South Africa the seldom flooded supratidal habitat that has halophytic species has been included as salt marsh and is considered a component of the estuary. The 5 m topographical contour is used to demarcate the estuarine functional zone (EFZ) and the lateral boundaries. Supratidal salt marsh occurs at > 1.5 m above mean sea level (amsl) and an ecotone with terrestrial species can occur from > 2.5 m amsl (Veldkornet 2015). The supratidal salt marsh may only be flooded twice a year during exceptional spring tide events (Adams et al., 1999). Other studies refer to this as the high marsh (Borman 2003). Thus a description of the distribution of salt marsh is influenced by its 1 definition. This has not been well described for the WIO region and information on this important habitat is lacking, posing a threat to conservation efforts. Salt marsh species are typically succulents and grasses with common species including Bassia diffusa, Sarcocornia mossambicensis, Sarcocornia natalensis, Suaeda spp., Sporobolus virginicus., Salicornia spp., Sesuvium portulacastrum and Juncus kraussii. Some of these species (e.g. Sarcocornia natalensis) extend from South Africa to the lower regions of Mozambique and Madagascar. Species common in Mozambique salt marshes are Arthrocnemon sp., Pemphis acidula, Portulaca oleracea, Salicornia sp., Sporobolus virginicus, Suaeda monoica and Suriana maritima. In Somalia species such as Urochondra setulosa occur; a halophytic grass found in North West Africa and South East Asia (Khan et al. 2009). Salicornia virginica is also common (Carbone and Accordi 2000). In Tanzania and Madagascar sea purslane Sesuvium partulacastrum and Suaeda monoica occur on soils too saline for mangrove species. The annual Salicornia pachystachya occurs from Kenya to South Africa, Madagascar and other Indian Ocean islands in salt marsh associated with mangrove swamps. It is clear that salt marsh species occur widely in the WIO although the overall habitat is poorly described. Distribution Distribution is discussed for only some of the WIO countries below, based on available information. Mozambique Salt marshes occur in most areas adjacent to mangroves and estuaries, but some occur further inland associated with the brackish lakes of southern Mozambique. Salt marshes are extensive in lowland areas and in areas with a wide tidal range with limited freshwater drainage or seepage. Large salt marshes are common in Maputo Bay, the Limpopo Estuary and areas around the estuaries of Cabo Delgado and Nampula provinces (Table 1). They also occur on the Changane River, a tributary of the Limpopo , where salt tolerant species such as Suaeda sp. and Salicornia sp. are found at Chibuto village near Xai-Xai town. In Maputo Bay salt marsh occurs in extensive areas between mangroves and terrestrial vegetation; generally in degraded mangroves and around coastal lakes (UNEP and WIOMSA 2015). Maputo Bay is surrounded by mangroves, but extensive areas, especially in the northern Maputo city regions of Bairro dos Pescadores, Mapulene and Muntanhana, are covered by salt marshes. Unfortunately, these areas have been heavily impacted by housing expansion. The Limpopo River Estuary supports extensive areas with grassy (Sporobolus virginicus) salt marshes. River flooding in 2000 halved the original mangrove areas enabling salt marsh colonisation (Bandeira and Balidy 2016). Lowland areas between the sea and mangroves near Inhambane Town are colonised by salt marsh. The small Chiveve River, that runs through Beira City in central Mozambique, supports extensive salt marshes, especially around the Beira Gold Club, and dominant species include Phragmites australis, Sporobolus virginicus, Cynodon dactylon, Panicum maximum, Pennisetum sp., Cyperus compressus and Urochloa mosambicensis. Quelimane (on the northernmost arm of the Zambezi Delta) has extensive grassland areas adjacent to mangroves, especially around the Chuabo Dembe area. Some salt marsh species occur 2 in the ecotone between the mangrove species and the grasses with species such as Sporobolus sp., Sezivium portulacatrum, Arthrocnemum sp. and Salicornia sp. present. Furthermore, it has been reported that new areas are being covered by sea water creating more habitat for colonisation by mangroves and salt marshes in the outer areas. There are also examples of salt marshes occurring in abandoned salt pans in areas near Quelimane, with adjacent areas such as Mirazane being used for rice farming. In northern Mozambique salt marshes occur in several places, but information is scarce. Salt marshes have been observed in Nacala Bay (Nampula), in areas around the Memba mangroves (particularly near the northern side of the Mecuburi Estuary), between Pemba Bay and Mecufi, and in Pemba Town, especially in the lowland area of Paquitequete. Some of the dominant species here include Suaeda monoica, Suriana maritima, Pemphis acidula and Sporobolus sp. Freshwater reeds and sedges also occur around some of these areas. The delta of the Montepuez Estuary in northern Mozambique (Figure 2) has extensive salt marshes. Fieldwork is needed to verify the diversity and extent of these habitats within the Montepuez Channel, facing the southern Quirimbas Archipelago. The area from the border with Tanzania to Pemba is part of the Pemba Bay-Mtwara ? , and also lies within the Mozambique Channel. Commented [TA1]: Ecotone? EBSA? Region? Commented [TA2]: Ecotone?, Table 1: Known salt marshes in Mozambique and estimates of area, habitat trend (increasing, decreasing, stable) and protection status. Location Region GPS Position Estimate of Habitat Pressures Protection status /Province Size (ha) trend Montepuéz Cabo -12.522175 S, unknown S Agriculture Quirimbas National 40.441883 E River Estuary Delgado Park Paquitequete, Cabo -12.959941 S, < 10 D Development None 40.487728 E Pemba Town Delgado Mecúfi Cabo -13.301508S, > 50 D Salt plans, None 40.538581E Delgado Road upgrade Memba Nampula Unknown S Salt pans None -14.165659 S, northern side 40.522386 E of Mecuburi Estuary Nacala Bay Nampula -14.582390 S, Unknown D Port None 40.619345 E development, town expansion Quelimane Zambezia -17.869956 S, > 80 I development, None 36.865297 E rice production Cabo São Inhambane -22.240042 S, Unknown S Area of total Sebastião 35.390492 E protection (private managed) 3 Limpopo Gaza -25.148213 S, > 300 ha S Flooding Community 33.518060 E Estuary managed wider mangrove area Maputo City Maputo -25.875712 S, > 500 ha D Urban None 32.658775 E development Saline lagoons and lakes, situated within a short distance from the coastline, are a common feature in southern Mozambique (south of Vilanculos region). From a geomorphological perspective these are mostly Pleistocene formations and are brackish or near freshwater. The vegetation in and around these lakes is dominated by Hibiscus tiliaceus, Phoenix reclinata, Phragmites australis, Ruppia maritima and Typha latifolia (Bandeira et al. 2007). The dominant succulent is Portulaca oleracea, though not all areas Commented [TA3]: Not in ref list surrounding these lakes qualify as salt marshes. Some of these areas lie adjacent to the Ecologically or Biologically Significant Area (EBSA) of Save-São Sebastian region (encompassing Bazaruto Archipelago and some inland swamps). Salt marsh habitat has also been identified in the Incomati-Ponta de Ouro EBSA that encompasses Maputo Bay, Lingamo (near Maputo and Port) and Inhaca Island, and in some areas near Saco da Inhaca. Macnae (1995) identified salt marshes adjacent to the airstrip at Inhaca Island. Madagascar The western and northern parts of Madagascar support large mangrove areas. Intertidal areas are generally wide and salt marsh occurs on the landward side of mangrove stands. Salt marshes occur near Tsangajoly, Toliara Province in southwestern Madagascar, while salt pans and associated marsh habitat also exists at Morondava on the west coast. Mudflats of up to 1 km wide occur together with mangroves, lakes and salt marshes in the Ambavanankarana wetlands along the western coast (Marnewick et al.